Renewable energy power sources, such as solar photovoltaic (PV) arrays and wind turbines, are connected into micro-grids that are part of an area Electric Power System (macro-grid). In the near future, an estimated 25% of renewable resources will be behind utility and customer owned micro-grids at 50% total renewable generation and thus will be a significant portion of the future electric power grid. There will be many participants with control of the renewable sources with little knowledge of the complex grid and how it is managed. Micro-grids are a collection of loads and generation sources that act as a single entity to the macro-grid and can connect and disconnect from the macro-grid seamlessly. The renewable energy resources (Solar PV, fuel cell, battery, wind) in a micro-grid have little or no inertia and hence are difficult to control compared to systems with high inertia from rotating energy sources like combustion turbines or conventional steam turbines powered by conventional fossil fuels such as coal or natural gas. The IEEE 1547.4 standards clearly point out the sensitivity of micro-grids to instability and voltage stability issues. Controlling the power characteristics of such micro-grids is an increasing problem, since variations in frequency or voltage can cause the micro-grid to be disconnected from the broader macro-grid. Micro-grids can be of any size, although they are generally less than 20 MW in size.